Re: cause of Gigantism in sauropods

["Habib, Michael" <MHabib@Chatham.edu>]

On Feb 7, 2011, at 10:05 AM, "vultur-10@neo.tamu.edu" <vultur-10@neo.tamu.edu> 
wrote:

>>> Another is that many sauropods "overshot": they are far larger than 
>>> required to be effectively immune to predation.
> 
> Are they? Even adult African elephants, which are *at least* 20x the mass of 
> lions, are occasionally killed by lions. Lone wolves can kill moose 10-15x 
> heavier. Was any sauropod actually 20x or more heavier than the largest 
> contemporaneous predator?

This why I used the term "effectively".  Elephants are killed by very large 
groups of desperate lions on very rare occasions.  The effective rate of adult 
mortality to predation among elephants is so small that the selective 
coefficient for larger size to escape predation in those animals must 
necessarily be tiny. I am not aware of confirmed accounts of lone wolves 
killing healthy adult moose; any references there would be great (sounds 
intense!).  I suspect it is a very rare event, as well.  

I get the impression that something in our general mode of thinking or culture 
has made the idea of vertebrate predators regularly killing prey many times 
larger than themselves seem intuitively reasonable, even though the data 
indicate strongly otherwise. Rates of such events are a bit higher for flying 
predators, but otherwise, cases of predators killing relatively giant prey 
appear to be exceptionally rare. The only "common" cases I know of are at the 
smaller end of the mammalian body size spectrum (weasels killing rabbits, for 
example).

Cheers,

--Mike H.